"Your sister is my friend."
Translation:आपकी बहन मेरी दोस्त है।
Great question! Following to see what the current, on the ground connotations may be in some people's experiences.
Saheli definitely sounds like in English a woman refers to her (platonic) "girlfriend." At breakfast: Dad says, "Where is that daughter of ours?! It must be 9:30 by now!" Mom says, "Oh, she went out last night to the roller rink with her girlfriends."
In the old days and conservative circles, if a dost... uh oh... So like a boy-dost, you mean? But then the male-gendered word "dost", for lack of better, became an OK thing to call a female friend. Notice however, that English "friend" is also said by people of the class who think boys and girls can be friends :) This is a common pattern of English words that replace "native" words (dost is Persian anyway) in order to create a fresh slate of connotations.
Possibly, but it (also) means female friend of a woman. https://www.shabdkosh.com/search-dictionary?e=saheli&lc=hi&sl=en&tl=hi
Instead of है I put हैं, just to see if it would be accepted. The reasoning is that since the woman who is the sister is the subject, and there is a possibility that she could be an older person. If she is older shouldn't we be more respectful with a हैं, like we say for मां, पिता, दादा और दादी..? Or am I making some mistake here..? Duolingo said my answer is wrong.
It is technically yes, but it's used as either according to the friend's gender.
It is technically a masculine noun, but unusual in that it adopts the gender of the person it refers to for purposes of inflecting the rest of the sentence.
To be more specific/unambiguous in sentence that didn't give that clue, a मित्र is a male friend and मित्रा a female friend.